When nil (the default for *case-sensitive-dde*) and a
case-insensitive Lisp is running, then any DDE topic and item names
are changed to the preferred string-case of the Lisp either before
converting them to symbols to use in Lisp or after converting them to
strings to pass to other DDE programs. So if another DDE application
passes the topic "LarrySanders" to Lisp, a
:case-insensitive-upper Lisp would handle the topic
name as the keyword :LARRYSANDERS and a
:case-insensitive-lower Lisp would handle the topic
name as the keyword :larrysanders. This is done by
default partly to make the printing and handling of the symbols more
convenient, and also because the documentation for some DDE programs
does not make it clear exactly what string-case they really use for
their topic and item names.

On the other hand, some DDE programs deal with topic and item names in
a case-sensitive way, though this is less common. If you need to
communicate with such a program from a case-insensitive Lisp, then you
will probably need to set either the *case-sensitive-dde* global default
or the case-sensitive-dde property for a
particular Lisp process to true. Then Lisp will not modify the
string-case at all when converting between symbols and DDE strings.